A mounting device is used to mount a handlebar on a head tube of a bicycle and includes a positioning member which is adapted to be mounted on the head tube and a holding member which includes complementary first and second holding arms. Each holding arm has a pivot end portion, a gripping end portion and an abutment face which extends between the pivot and gripping end portions. The pivot end portion of each of the holding arms is mounted pivotally on the positioning member. The gripping end portion of each of the holding arms is formed with a grip section with an axis that is parallel to an axis of the pivot hole. The grip sections of the holding arms are adapted to grip fittingly the handlebar therebetween. The abutment faces of the holding arms are complementary and are formed as twisted faces that abut against each other. A first fastener extends through the pivot end portion of each of the holding arms and the positioning member to mount the holding member onto the positioning member. A second fastener extends through the holding arms on one side of the grip section to secure the holding member on the handlebar.